1. Field of the Invention
The present invention relates to a press apparatus and method for pressing water from a paper web. More particularly, the present invention relates to an extended nip press for pressing water from a paper web.
2. Information Disclosure Statement
In the papermaking art, a web of paper is formed by ejecting stock onto a moving screen such that water is drained through the screen so that a fibrous web is formed thereon. The fibrous web is removed from the screen and is guided through at least one pair of counter- rotating rolls for pressing excess water from the formed web.
More recently, it was discovered that by increasing the residence time of the web within the pressing section, more water could be removed from the formed web, thereby reducing the amount of thermal energy required in any subsequent drying section. Accordingly, such proposals generally include a rotatable backing roll and a cooperating shoe defining a concave surface for cooperation with the backing roll to define therebetween an extended nip.
In order to enable the formed web to extend through the extended nip, the aforementioned extended nip press includes an endless looped bearing blanket which slidably cooperates with the concave surface of the shoe so that the web and blanket extend through the extended pressing section, thereby increasing the residence time of the web within the pressing section.
Not only is the residence time of the web within the pressing section increased, but also the web is subjected to a less severe increase in pressure during passage of the web through the extended nip. Accordingly, the extended nip press not only increases the amount of water removed from the formed web, but also enhances the properties of the resultant web.
However, although the aforementioned extended nip press concept is comparatively straight-forward, the production of a commercially feasible extended nip press involves considerable technological problems and the expenses associated therewith.
Accordingly, the present invention provides an apparatus for increasing the residence time of the formed web during passage through a pressing nip while avoiding the complexities associated with the aforementioned extended nip press arrangements.
The present invention provides a press apparatus which includes a pair of press rolls, at least one of which rolls is covered with an elastomeric covering such that the pressing nip is extended in a machine direction so that the residence time of the web during passage of the web through the nip is increased.
Therefore, it is a primary objective of the present invention to provide a press apparatus and method which overcomes the aforementioned inadequacies of the prior art arrangements and which makes a considerable contribution to the art of pressing water from a paper web.
Another object of the present invention is the provision of a press apparatus having a first press roll having a concentric cover and heating means for conducting heat to the web such that the web is subjected to increased pressure and temperature for an extended period.
Another object of the present invention is the provision of a press apparatus in which the uncovered press roll defines a porous outer surface which is heated.
Another object of the present invention is the provision of a press apparatus in which at least one of the press rolls is covered with an elastomeric cover and wherein the web is heated by means of a heat conductive belt such that the belt conducts heat to the web during movement of the web and the belt through the pressing nip.
Another object of the present invention is the provision of a press apparatus which includes an elastomeric blanket defining an endless loop, the blanket extending through an extended nip defined between a pair of rolls, at least one of which is covered with an elastomeric cover such that the residence time within the pressing nip is further increased.
Another object of the present invention is the provision of a press apparatus which includes a guiding means for guiding an elastomeric blanket such that the blanket and web wrap around a portion of a porous outer surface of one of the press rolls in order to adjust the pressure profile of the web exiting the pressing nip.
Another object of the present invention is the provision of a press apparatus including insulating means for inhibiting the conduction of heat from a heating means to an elastomeric cover covering at least one press roll.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.